In the manufacture of semiconductor devices and other articles through coating or etching processes performed on wafers and other substrates, it is imperative that the contamination of the substrate surfaces to be processed be minimized. Surfaces to be protected from such contamination include, for example, the device surfaces of semiconductor wafers. The device surfaces are the surfaces of the wafers on which layers of conductive, insulative or other material are coated or etched by sputtering or other processes to form the manufactured devices. In such processes, the presence of microscopic contaminants on the device surface of a wafer may render an entire device functionally defective by adversely affecting the application or removal of a component layer at a critical point on the wafer surface.
Similarly, magnetic disks, optical disks, lenses, magneto-optical disks and other such objects may be substantially reduced in value or quality by contaminants present on the surface during processing. In the manufacture of large scale integrated circuits, a large quantity of semiconductor devices is formed of a single wafer. In the processing of such wafers, the contaminants present on the device surface of a wafer during processing can significantly reduce the number of such devices of acceptable quality produced from the wafer.
In a semiconductor processing apparatus such as a typical sputter coating or sputter etching machine, a wafer substrate is processed in an isolated and usually near vacuum environment. Such machines have a vacuum chamber in which the processing operations are carried out. The vacuum chamber is usually provided with one or more chamber doors located in the wall of the chamber through which wafers being processed are introduced and removed. On the outside of this chamber, the wafers are moved by some wafer handling mechanism between a cassette or carrier and the chamber door. A transfer mechanism, which is usually included in the external wafer handling mechanism, introduces the wafers into and removes them from the vacuum chamber through the chamber door opening. In the vacuum chamber, the wafer is usually received and held by a holder that supports the wafer during processing.
During the entry and removal of the wafers from the vacuum chamber, the portion of the chamber into which the wafers are placed and from which the wafer is removed will necessarily be at the same pressure and of the same atmospheric environment as exists in the external environment outside the chamber door. Such external environment will almost always contain air or some other gas containing some amount of water vapor. During processing, however, the portion of the chamber in which the wafer is to be processed must be brought to the vacuum pressure and atmospheric content as the process requires. This change of atmospheres necessitates a repetitive opening and isolation of the internal and external environments and the alternate pumping and venting o at least a portion of the vacuum chamber.
Wafer processing machines that process wafers in a vacuum environment most often maintain a constant vacuum environment so that processing upon some wafers can be carried out as others are being inserted into or removed from the chamber. To this end, such machines have an intermediate chamber or load lock at the entry to the processing chamber that alternately communicates with the external environment through the open chamber door, and, when the door is sealed, with the internal environment of the processing chamber through a sealable entry thereto. Such a load lock is alternately pumped to the vacuum level of the internal environment of the main processing chamber and vented to the external environment so that the pressure of the load lock matches that of environment with which it communicates during the introduction into and removal from the processing chamber of the wafers. With such a load lock, the internal portion of the chamber where processes are carried out may be maintained continuously at the pressure and composition of the vacuum environment and may be used additionally for the processing of other wafers while wafers are being introduced into and removed from the load lock chamber.
Other types of processing machine, such as batch processing machines may have no load lock, but are instead opened to the external environment and loaded with the objects to be processed. In such machines, the entire processing chamber is repeatedly pumped and vented.
After a chamber is loaded and sealed, it is necessary to pump the chamber to a near vacuum level. To maintain high productivity, the atmosphere should be pumped from the chamber as rapidly as possible. This pumping, when it is done rapidly, often causes moisture contained in the air within the chamber to momentarily condense, forming a temporary fog in the chamber. This condensate can precipitate onto the surface to be processed of the object within the chamber. This moisture, when it evaporates from the object surface, often leaves a microscopic residue. This residue can contaminate the surface to be processed, which can cause defective processing of the object to occur.
Accordingly, there is a need to reduce the contamination by condensation of water vapor of semiconductor wafer disks, and other objects in load locks and other pressure chambers of processing machines when rapid pumping of the chamber containing the object to a near vacuum level is occurring.